A display device is installed in a vehicle for displaying a map around a current location of the vehicle, traffic or road information, and television pictures. A liquid crystal display (LCD) is commonly used in such a display device. The LCD has characteristics of a slow response under a low temperature due to characteristics of a liquid crystal material. Images on the LCD look blurry when the response of the LCD is slow, that is, at the low temperature. Therefore, it will take a while until the LCD is warmed up by a room heater to an appropriate temperature for providing clear images when the vehicle is started under a low temperature.
To solve this problem, a heater may be provided in the display device. The LCD is not warmed up immediately after an accessory switch of an ignition switch system is turned on and the heater is turned on. As a result, the images still look blurry at the start of the vehicle even when the heater is provided.
A heater for preheating a cold cathode fluorescent tube is proposed in JP-A-9-48281. The heater starts heating the cold cathode fluorescent tube when an unlocking of a vehicle door is detected. Thus, the cold cathode fluorescent tube is heated prior to a start of a vehicle. However, it will take longer to warm up the LCD. Therefore, the LCD may not be warmed up to the appropriate temperature when the warm-up of the LCD is started upon the detection of the unlocking of the vehicle door.